Methods of forming a staircase structure

ABSTRACT

Methods of improving adhesion between a photoresist and conductive or insulating structures. The method comprises forming a slot through at least a portion of alternating conductive structures and insulating structures on a substrate. Portions of the conductive structures or of the insulating structures are removed to form recesses in the conductive structures or in the insulating structures. A photoresist is formed over the alternating conductive structures and insulating structures and within the slot. Methods of improving adhesion between a photoresist and a spin-on dielectric material are also disclosed, as well as methods of forming a staircase structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/531,815, filed Aug. 5, 2019, now U.S. Pat. No. 10,930,659, issuedFeb. 23, 2021, which is a continuation of U.S. patent application Ser.No. 15/624,422, filed Jun. 15, 2017, now U.S. Pat. No. 10,600,796,issued Mar. 24, 2020, the disclosure of each of which is herebyincorporated herein in its entirety by this reference.

TECHNICAL FIELD

Embodiments disclosed herein relate to semiconductor fabricationincluding methods of forming semiconductor structures includingstaircase structures. More particularly, embodiments of the disclosurerelate to methods of improving adhesion between photoresist or spin-ondielectric materials and adjacent materials in the staircase structures.

BACKGROUND

A continuing goal of the semiconductor industry has been to increase thememory density (e.g., the number of memory cells per memory die) ofmemory devices, such as non-volatile memory devices (e.g., NAND Flashmemory devices). One way of increasing memory density in non-volatilememory devices is to implement vertical memory array (also referred toas a “three-dimensional (3D) memory array”) architectures. Aconventional vertical memory array includes transistor/memory-cellpillars extending through openings in repeating conducting/insulatingstructures films (e.g., tiers), where the conducting structures functionas control gates. The vertically stacked tiers of conductive structures(e.g., word line plates, control gate plates) and insulating structuresat each junction of the semiconductor pillars and the conductivestructures. Such a configuration permits a greater number of transistorsto be located in a unit of die area by building the array upwards (e.g.,longitudinally, vertically) on a die, as compared to structures withconventional planar (e.g., two-dimensional) arrangements of transistors.

Conventional vertical memory arrays include electrical connectionsbetween the conductive structures and access lines (e.g., word lines) sothat memory cells in the vertical memory array can be uniquely selectedfor writing, reading, or erasing operations. One method of forming suchan electrical connection includes forming a so-called “staircase”structure having so-called “stairs” at edges (e.g., lateral ends) of thetiers of conductive structures. The stairs are formed by etching exposedregion of the conductive structures. The individual stairs definecontact regions of the conductive structures upon which contactstructures can be positioned to provide electrical access to theconductive structures. Various processes of forming staircase structureshave been developed.

In one such fabrication process, a slot is formed in the alternatingconductive structures and insulating structures before forming thestaircase structure. Alternating conductive structures and insulatingstructures 2 are formed on a substrate (not shown) and a slot 14 isformed in the center of at least a portion of the alternating conductivestructures and insulating structures 2, as shown in FIG. 1 . Forsimplicity, the alternating conductive structures and insulatingstructures 2 are shown in FIG. 1 as a single material. The slot 14extends from an uppermost surface of the alternating conductivestructures and insulating structures 2 and into the alternatingconductive structures and insulating structures 2 to a depth D1. Theslot 14 also has a length L1 and a width W1. The slot 14 is defined bysidewalls 15 of the conductive structures and insulating structures 2and a bottom surface 17 of the conductive structures and insulatingstructures 2. The sidewalls 15 are substantially vertical surfaces ofexposed portions of the conductive structures and insulating structures2 within the slot 14. The portion of alternating conductive structuresand insulating structures 2 has a length L2 and a width W2.

A photoresist 18 is formed over the uppermost surface of the conductivestructures and insulating structures 2 laterally adjacent to the slot14, and over the sidewalls 15 and the bottom surface 17 of thealternating conductive structures and insulating structures 2 within theslot 14, as shown in FIG. 2 . The photoresist 18, thus, contacts thesidewalls 15 of the conductive structures and insulating structures 2.Due to the large volume of photoresist 18 used and shrinkage in thephotoresist 18 during and after its formation, delamination may occur atthe sidewalls 15. The delamination may also be caused by poor adhesionbetween the photoresist 18 and the alternating conductive structures andinsulating structures 2. As also shown in FIG. 2 , because of thedelamination, a so-called “creek” 19 may form along the bottom region ofthe sidewalls 15 of the slot 14 formed in the alternating conductivestructures and insulating structures 2. Although not shown in FIG. 2 forsimplicity, the creek 19 may also form throughout the sidewalls 15 ofthe slot 14 formed in the alternating conductive structures andinsulating structures 2. A scanning electron micrograph (SEM) showingthe photoresist 18 delaminating from the sidewalls 15 of the alternatingconductive structures and insulating structures 2 is shown in FIG. 3 .

As shown in FIG. 4A, a portion of the photoresist 18 is removed (e.g.,etched, trimmed) by conventional photolithography techniques, such as bya dry etch process, to form an opening 21 in the photoresist 18. Theopening 21 exposes vertical surfaces 22 of the photoresist 18. Theexposure, bake, and development acts involved in the dry etch processmay cause the photoresist 18 to shrink further, widening the creek 19 toform a void 23 between the sidewalls 15 of the alternating conductivestructures and insulating structures 2 and the photoresist 18. Theetchants of the dry etch process may enter the creek 19, widening thecreek 19 and forming the void 23. The creek 19 may be enclosed withinthe bulk of the photoresist 18/sidewall 15 interface and may not bevisible during non-destructive imaging. FIG. 4B shows the creek 19visible at the photoresist 18/sidewall 15 interface as it extends up tothe surface 22. During the subsequent dry etch process, the conductivestructures and insulating structures 2 exposed by the opening 21 areetched vertically and the photoresist 18 is trimmed, causing surface 22to move laterally and causing the opening 21 to widen. The repeatingetch-trim processes creates multiple “stair” like steps in thealternating conductive structures and insulating structures 2, whichresults in the “staircase” structure. Under the plasma conditions of thedry etch process during the staircase formation, the etchants/reactionbyproducts of the etch may enter (e.g., fill) the creek 19, etching thephotoresist 18 in the creek 19, continuously widening the creek 19, andforming the void 23, shown in FIG. 5 . Stairs subsequently formedadjacent to the void 23 have the same profile of the photoresist 18,which results in the formation of deformed stairs in the staircasestructure. The void 24 results in deformation (e.g., change) in theprofile of the portion of photoresist surface 22 adjacent to thesidewalls 15. A portion of stairs subsequently formed adjacent to thesidewall 15 have the same deformed profile projected from the deformedphotoresist surface 22, which results in the formation of deformed stairregion 28 in the staircase structure. An SEM of the resulting staircasestructure 25 is shown in FIGS. 5A and 5B, with a region including thedeformed stairs circled and the void 23 shown. Since the stairs have theundesired deformed profile which is not consistent in shape, contactstructures (not shown) subsequently formed on these stairs are notproperly aligned, causing failure of a device including the staircasestructure. In other words, the contact structures land unreliably on theincorrect conductive plates, causing the device failure. To avoid devicefailure, changes to the fabrication process have been made. However,these changes add considerable expense and time to the fabricationprocess.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 4A, and 4B are simplified, plan views illustrating initialacts in a conventional process of fabricating a staircase structure;

FIG. 3 is a scanning electron micrograph (SEM) showing the structure ofFIG. 2 formed during the conventional process of fabricating thestaircase structure;

FIGS. 5A and 5B are SEMs of a staircase structure formed by theconventional process;

FIGS. 6-9 are cross-sectional views showing the fabrication process of astaircase structure in accordance with embodiments of the disclosure;

FIG. 10A is an SEM showing improved adhesion between a photoresist andtier materials in accordance with embodiments of the disclosure and FIG.10B is an enlarged view of FIG. 10A;

FIG. 11 is an SEM of a staircase structure formed in accordance withembodiments of the disclosure; and

FIG. 12 is a cross-sectional view showing the fabrication process of astaircase structure in accordance with another embodiment of thedisclosure.

DETAILED DESCRIPTION

Methods of improving adhesion between a photoresist and alternatingconductive structures and insulating structures of a staircase structureare described, as are methods of forming semiconductor device structures(e.g., memory array blocks) including staircase structures that have thephotoresist and the alternating conductive structures and insulatingstructures. The fabrication of the staircase structures includes forminga slot having large dimensions in the alternating conductive structuresand insulating structures. Recesses are formed in the conductivestructures or in the insulating structures, laterally adjacent to theslot. A photoresist is formed over the conductive structures andinsulating structures, including within the slot and recesses. Therecesses enable increased adhesion between the photoresist and materialsof the conductive structures and insulating structures. The improvedadhesion enables the formation of stairs and contact structures on thestairs that are aligned. The staircase structure formed by the methodsof the disclosure has reduced numbers of defects in the contactstructures on the stairs. Thus, failure of a device including thestaircase structure is reduced or eliminated compared to a device formedby a conventional process of forming the staircase structure.

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments described herein. However,a person of ordinary skill in the art will understand that theembodiments disclosed herein may be practiced without employing thesespecific details. Indeed, the embodiments may be practiced inconjunction with conventional fabrication techniques employed in thesemiconductor industry. In addition, the description provided hereindoes not form a complete description of a semiconductor structure or acomplete process flow for manufacturing semiconductor device structuresand the structures described below do not form a complete semiconductordevice structure. Only those process acts and structures necessary tounderstand the embodiments described herein are described in detailbelow. Additional acts to form a complete semiconductor device structuremay be performed by conventional techniques.

Drawings presented herein are for illustrative purposes only, and arenot meant to be actual views of any particular material, component,structure, device, or system. Variations from the shapes depicted in thedrawings as a result, for example, of manufacturing techniques and/ortolerances, are to be expected. Thus, embodiments described herein arenot to be construed as being limited to the particular shapes or regionsas illustrated, but include deviations in shapes that result, forexample, from manufacturing. For example, a region illustrated ordescribed as box-shaped may have rough and/or nonlinear features, and aregion illustrated or described as round may include some rough and/orlinear features. Moreover, sharp angles that are illustrated may berounded, and vice versa. Thus, the regions illustrated in the figuresare schematic in nature, and their shapes are not intended to illustratethe precise shape of a region and do not limit the scope of the presentclaims. The drawings are not necessarily to scale. Additionally,elements common between figures may retain the same numericaldesignation.

As used herein, the terms “vertical,” “longitudinal,” “horizontal,” arein reference to a major plane of a structure and are not necessarilydefined by earth's gravitational field. A “horizontal” or “lateral”direction is a direction that is substantially parallel to the majorplane of the structure, while a “vertical” or “longitudinal” directionis a direction that is substantially perpendicular to the major plane ofthe structure. The major plane of the structure is defined by a surfaceof the structure having a relatively large area compared to othersurfaces of the structure.

As used herein, spatially relative terms, such as “beneath,” “below,”“lower,” “bottom,” “above,” “upper,” “top,” “front,” “rear,” “left,”“right,” and the like, may be used for ease of description to describeone element's or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. Unless otherwise specified,the spatially relative terms are intended to encompass differentorientations of the materials in addition to the orientation depicted inthe figures. For example, if materials in the figures are inverted,elements described as “below” or “beneath” or “under” or “on bottom of”other elements or features would then be oriented “above” or “on top of”the other elements or features. Thus, the term “below” can encompassboth an orientation of above and below, depending on the context inwhich the term is used, which will be evident to one of ordinary skillin the art. The materials may be otherwise oriented (e.g., rotated 90degrees, inverted, flipped) and the spatially relative descriptors usedherein interpreted accordingly.

As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

As used herein, “and/or” includes any and all combinations of one ormore of the associated listed items.

As used herein, the term “configured” refers to a size, shape, materialcomposition, and arrangement of one or more of at least one structureand at least one apparatus facilitating operation of one or more of thestructure and the apparatus in a pre-determined way.

As shown in FIG. 6 , a semiconductor structure 100 from which thestaircase structure is to be formed may include a substrate 102, andalternating conductive structures 106 and insulating structures 108arranged in tiers 110 over the substrate 102. For clarity and ease ofunderstanding of the drawings and related description, FIG. 6 shows five(5) tiers 110 of the conductive structures 106 and the insulatingstructures 108. A first tier 110 a includes a first conductive structure106 a and a first insulating structure 108 a over the first conductivestructure 106 a; a second tier 110 b overlies the first tier 110 a, andincludes a second conductive structure 106 b and a second insulatingstructure 108 b over the second conductive structure 106 b; a third tier110 c overlies the second tier 110 b, and includes a third conductivestructure 106 c and a third insulating structure 108 c over the thirdconductive structure 106 c; a fourth tier 110 d overlies the third tier110 c, and includes a fourth conductive structure 106 d and a fourthinsulating structure 108 d over the fourth conductive structure 106 d;and a fifth tier 110 e overlies the fourth tier 110 d, and includes afifth conductive structure 106 e and a fifth insulating structure 108 eover the fifth conductive structure 106 e. However, the semiconductorstructure 100 may include a different number of tiers 110. For example,in additional embodiments, the semiconductor structure 100 may includegreater than five (5) tiers 110 (e.g., greater than or equal to ten (10)tiers 110, greater than or equal to twenty-five (25) tiers 110, greaterthan or equal to fifty (50) tiers 110, greater than or equal to onehundred (100) tiers 110, greater than or equal to five hundred (500)tiers 110, or greater than or equal to one thousand (1000) tiers 110) ofthe conductive structures 106 and the insulating structures 108, or mayinclude less than five (5) tiers 110 (e.g., less than or equal to three(3) tiers 110) of the conductive structures 106 and the insulatingstructures 108.

As used herein, the term “substrate” means and includes a base materialor construction upon which additional materials are formed. Thesubstrate may be a semiconductor substrate, a base semiconductor layeron a supporting structure, a metal electrode, or a semiconductorsubstrate having one or more materials, layers, structures, or regionsformed thereon. The materials on the semiconductor structure mayinclude, but are not limited to, semiconductive materials, insulatingmaterials, conductive materials, etc. One or more of the materials maybe thermally sensitive. The substrate may be a conventional siliconsubstrate or other bulk substrate comprising a layer of semiconductivematerial. As used herein, the term “bulk substrate” means and includesnot only silicon wafers, but also silicon-on-insulator (“SOI”)substrates, such as silicon-on-sapphire (“SOS”) substrates andsilicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on abase semiconductor foundation, and other semiconductor or optoelectronicmaterials, such as silicon-germanium, germanium, gallium arsenide,gallium nitride, and indium phosphide. The substrate may be doped orundoped.

The conductive structures 106 may be formed of and include at least oneconductive material, such as a metal (e.g., tungsten, titanium,molybdenum, niobium, vanadium, hafnium, tantalum, chromium, zirconium,iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium,platinum, copper, silver, gold, aluminum), a metal alloy (e.g., acobalt-based alloy, an iron-based alloy, a nickel-based alloy, an iron-and nickel-based alloy, a cobalt- and nickel-based alloy, an iron- andcobalt-based alloy, a cobalt- and nickel- and iron-based alloy, analuminum-based alloy, a copper-based alloy, a magnesium-based alloy, atitanium-based alloy, a steel, a low-carbon steel, a stainless steel), aconductive metal-containing material (e.g., a conductive metal nitride,a conductive metal silicide, a conductive metal carbide, a conductivemetal oxide), a conductively-doped semiconductor material (e.g.,conductively-doped silicon, conductively-doped germanium,conductively-doped silicon germanium), or combinations thereof. In oneembodiment, the conductive structures 106 are formed from polysilicon.The conductive structure 106 may, for example, be formed of and includea stack of at least two different conductive materials. The conductivestructures 106 may each be substantially planar, and may eachindependently exhibit any desired thickness. The thickness of each ofthe conductive structures 106 may range from about 1 nm to about 1000nm, such as from about 1 nm to about 500 nm, from about 10 nm to about500 nm, or from about 10 nm to about 250 nm. In one embodiment, thethickness of the conductive structures 106 ranges from about 10 nm toabout 100 nm.

Each of the conductive structures 106 may be substantially the same(e.g., exhibit substantially the same material composition, averagegrain size, material distribution, size, and shape) as one another, orat least one of the conductive structures 106 may be different (e.g.,exhibit one or more of a different material composition, a differentaverage grain size, a different material distribution, a different size,and a different shape) than at least one other of the conductivestructures 106. As a non-limiting example, each of the first conductivestructure 106 a, the second conductive structure 106 b, the thirdconductive structure 106 c, the fourth conductive structure 106 d, andthe fifth conductive structure 106 e may exhibit substantially the samematerial composition, material distribution, and thickness. In someembodiments, each of the conductive structures 106 is substantially thesame as each other of the conductive structures 106.

The insulating structures 108 may be formed of and include at least oneinsulating material, such as an oxide material (e.g., silicon dioxide,phosphosilicate glass, borosilicate glass, borophosphosilicate glass,fluorosilicate glass, titanium dioxide, zirconium dioxide, hafniumdioxide, tantalum oxide, magnesium oxide, aluminum oxide, or acombination thereof), a nitride material (e.g., silicon nitride), anoxynitride material (e.g., silicon oxynitride), amphorous carbon, or acombination thereof. In one embodiment, the insulating structures 108are formed from a silicon oxide, such as silicon dioxide. The insulatingstructure 108 may also, for example, be formed of and include a stack(e.g., laminate) of at least two different insulating materials. Theinsulating structures 108 may each be substantially planar, and may eachindependently exhibit any desired thickness. The thickness of each ofthe insulating structures 108 may range from about 1 nm to about 1000nm, such as from about 1 nm to about 500 nm, from about 10 nm to about500 nm, or from about 10 nm to about 250 nm. In one embodiment, thethickness of the insulating structures 108 ranges from about 10 nm toabout 100 nm.

Each of the insulating structures 108 may be substantially the same(e.g., exhibit substantially the same material composition, materialdistribution, size, and shape) as one another, or at least one of theinsulating structures 108 may be different (e.g., exhibit one or more ofa different material composition, a different material distribution, adifferent size, and a different shape) than at least one other of theinsulating structures 108. As a non-limiting example, each of the firstinsulating structure 108 a, the second insulating structure 108 b, thethird insulating structure 108 c, the fourth insulating structure 108 d,and the fifth insulating structure 108 e may exhibit substantially thesame material composition, material distribution, and thickness. In someembodiments, each of the insulating structures 108 is substantially thesame as each other of the insulating structures 108.

The materials of the conductive structures 106 and the insulatingstructures 108 may be selected such that the conductive structures 106and the insulating structures 108 are selectively etchable relative toone another.

As shown in FIG. 6 , the conductive structures 106 and the insulatingstructures 108 are arranged in an alternating sequence on the substrate102 beginning with one of the conductive structures 106. However, theconductive structures 106 and the insulating structures 108 may bearranged in a different sequence, such as beginning with one of theinsulating structures 108. Accordingly, each of the tiers 110 mayalternatively include one of the conductive structures 106 on or overone of the insulating structures 108. A semiconductor device (e.g., avertical memory device, such as a 3D NAND Flash memory device; acrosspoint memory device, such as a 3D crosspoint memory device)employing a semiconductor device structure having such a configurationmay have little or no difference in terms of functionality oroperability as compared to a semiconductor device employing thearrangement of the conductive structures 106 and the insulatingstructures 108 shown in FIG. 6 .

The substrate 102, the conductive structures 106, and the insulatingstructures 108 may each independently be formed using conventionalprocesses including, but not limited to, physical vapor deposition(“PVD”), chemical vapor deposition (“CVD”), atomic layer deposition(“ALD”), and/or spin-coating. PVD includes, but is not limited to, oneor more of sputtering, evaporation, precursor spin-coating/calcination,and ionized PVD. Such processes are known in the art and, therefore, arenot described in detail herein.

After forming the conductive structures 106 and the insulatingstructures 108, a portion of the conductive structures 106 and theinsulating structures 108 is removed to form a slot 114 having a widthW3 and a depth D3, as shown in FIG. 7 . The slot 114 may be formed inthe center of the tiers 110, similar to that shown in FIG. 1 . While notshown in the perspective of FIG. 7 , the slot also has a length L3. Thelength L3 of the slot 114 is less than the length L2 of the conductivestructures 106 and the insulating structures 108. The length L3 of theslot 114 may depend on a length of the staircase ultimately to beformed. The width W3 of the slot 114 may be less than the width W2 ofthe conductive structures 106 and the insulating structures 108. Thewidth W3 of the slot 114 may depend on a width of the staircaseultimately to be formed. The depth D3 of the slot 114 may besubstantially equal to the depth D1 of the conductive structures 106 andthe insulating structures 108. While FIG. 7 shows that the slot 114 issubstantially centered across a width and length of the tiers 110, theposition of the slot 114 may be different depending on the desiredposition of the staircase(s) ultimately to be formed. The slot 114 isformed by conventional techniques, exposing sidewalls 115 of theconductive structures 106 and the insulating structures 108, which aresubstantially vertical. A bottom surface 117 of the conductivestructures 106 or of the insulating structures 108 is also exposed.

Portions of the conductive structures 106 or of the insulatingstructures 108 within the slot 114 may be selectively removed, formingrecesses 116 in the conductive structures 106, as shown in FIG. 8A, orin the insulating structures 108, as shown in FIG. 8B. The portions ofthe conductive structures 106 a-106 e laterally adjacent to the slot 114may be removed to form the recesses 116, creating a so-called “jagged”or “sawtooth” profile of the sidewalls 115 of the conductive structures106 a-106 e and the insulating structures 108 a-108 e. The jaggedprofiles of the sidewalls 115 provide an increased surface area to theconductive structures 106 or to the insulating structures 108 in theslot 114 compared to the sidewalls 15 shown in FIG. 1 . While FIG. 8Ashows the recesses 116 in the conductive structures 106 havingsubstantially planar (e.g., substantially vertical) and smooth surfaces,the surfaces may be nonplanar (e.g., curved, jagged) and rough. Byremoving portions of the conductive structures 106, the exposed surfacearea of the insulating structures 108 within the slot 114 is increased.Conversely, by removing portions of the insulating structures 108laterally adjacent to the slot 114 and forming recesses in theinsulating structures 108, the exposed surface area of the conductivestructures 106 within the slot 114 is increased.

Dimensions of the recesses 116 may be sized and configured such that aphotoresist may enter the recesses 116, as described in detail below. Awidth W4 of the recesses 116 may be from about 1 nm to about 100 nm fromthe sidewalls 115 of the slot 114. The dimensions of the recesses 116may be optimized depending on the desired degree of adhesion between thephotoresist and the conductive structures 106 and the insulatingstructures 108. Without being bound by any theory, larger dimensions ofthe recesses 116 may enable increased adhesion of the photoresist to theconductive structures 106 and the insulating structures 108 byincreasing the surface area of the conductive structures 106 and theinsulating structures 108 to which the photoresist 118 adheres. A heightof the recesses 116 may be determined by the thickness at which theconductive structures 106 or the insulating structures 108 are formedand a length of the recesses 116 may be determined by the length L3 ofthe slot 114. Since the height and length of the recesses 116 are set bythe desired dimensions of the staircase structure, increasing the widthW4 of the recesses 116 increases the degree of photoresist adhesion.

The recesses 116 in the conductive structures 106 or in the insulatingstructures 108 are formed by selectively removing portions of theconductive structures 106 or of the insulating structures 108 by an etchprocess, such as a wet etch process or an isotropic, selective dry etchprocess. The selective wet etch process isotropically removes a portionof the conductive structures 106 or a portion of the insulatingstructures 108 adjacent to the slot 114, without substantially removingthe portion of the insulating structures 108 or of the conductivestructures 106, respectively. Since the wet etch process is isotropic,portions of the conductive structures 106 or the insulating structures108 laterally adjacent to the slot 114 are selectively removed. The wetetch process may be conducted for an amount of time sufficient to formthe recesses 116 at the desired width.

Conventional wet etch chemistries may be used to form the recesses 116and may be selected depending on the materials used for the conductivestructures 106 and the insulating structures 108. In one embodiment, theconductive structures 106 are formed of polysilicon and the insulatingstructures 108 are formed of silicon dioxide. By way of example only, toform the recesses 116 in polysilicon, a conventional buffered oxide etch(BOE) solution followed by a conventional tetramethylammonium hydroxide(TMAH) solution may be used as the wet etchants. The BOE solution mayinclude hydrogen fluoride (HF) and ammonium fluoride (NH₄F) in water, asknown in the art, and removes native oxide on the polysilicon surface.The TMAH solution removes the portions of the polysilicon, forming therecesses 116 in the polysilicon. The TMAH solution may include TMAH andwater as known in the art. To form the recesses 116 in the silicondioxide, a conventional BOE solution may be used as the wet etchant.However, other conventional wet etchants selective for polysilicon orsilicon dioxide may be used in forming the recesses 116.

After forming the recesses 116, a photoresist 118 is formed over thetiers 110, including within the slot 114 and the recesses 116, as shownin FIG. 9 . The photoresist 118 may be formed over horizontal surfacesof the fifth (e.g., uppermost) tier 110 e of the conductive structures106 e and the insulating structures 108 e, over vertical surfaces of thetiers 110 a-110 d of the conductive structures 106 a-106 d and theinsulating structures 108 a-108 d exposed within the slot 114, andwithin the recesses 116. A viscosity of the photoresist 118 may be suchthat the photoresist 118 flows over the tiers 110 and into the slot 114and the recesses 116. The photoresist 118 may be a conventional 193 nmresist, a conventional 248 nm resist, a conventional 365 nm resist, or aconventional deep ultraviolet (DUV) resist. The photoresist 118 mayexhibit a positive tone or a negative tone.

The photoresist 118 may be formed over the tiers 110 at a thicknesssufficient to conduct the repeated trim acts utilized during subsequentacts to form the staircase structure. The photoresist 118 may, forexample, be spin-coated over the tiers 110. While the photoresist 118 isshown as partially filling the slot 114, the photoresist 118 maysubstantially fill the slot 114. The pattern formed in the photoresist118, after exposure and development, may serve as a mask to enableselective removal of (e.g., etch) portions of the tiers 110 of theconductive structures 106 and the insulating structures 108 to form thestaircase structure. The pattern in the photoresist 118 may be formedorthogonal to the length of the slot. A thickness of the photoresist 118may range from about 1 μm to about 10 μm, such as from about 8 μm toabout 11 μm. At a thickness within this range and the relatively largearea over which the photoresist 118 is formed, a large volume ofphotoresist 118 is used, which includes a large volume of solvent thatneeds to be removed during the application of the photoresist 118 andduring pattern formation in photoresist 118 using photolithography orother lithography methods. The large volume and thickness of photoresist118 utilized during the formation of the staircase structures isbelieved to contribute to the shrinkage and stress in the photoresist118, causing delamination of the photoresist 118 from the sidewall 115.The delamination may also be caused by poor adhesion properties of thephotoresist 118 to the conductive structures 106 and insulatingstructures 108. However, when the staircase structure is formed by amethod according to the embodiments of the disclosure, the photoresist118 may adhere to the conductive structures 106 and the insulatingstructures 108. Without being bound by any theory, it is believed thatthe increased surface area of the recesses 116 in the conductivestructures 106 or in the insulating structures 108 improves the adhesionof the photoresist 118 to the conductive structures 106 and theinsulating structures 108. The improved adhesion reduces or eliminatesdelamination of the photoresist 118, which reduces or eliminatesdefectively-formed stairs. Therefore, the staircase structure formedaccording to the embodiments of the disclosure may be substantially freeof defects in the stairs of the staircase structure.

Additional process acts may be conducted to form a completesemiconductor device structure including the staircase structure.Additional process acts for fabricating the staircase structure and thecomplete semiconductor device structure may be conducted by conventionaltechniques, which are not described in detail herein. The repeatedphotoresist trim acts may be utilized to form the staircase structure.Generally, during each trim act, additional photoresist 118 is removedand the underlying conductive structures 106 and insulating structures108 are etched using the remaining photoresist 118 as a mask. Followingcompletion of the staircase structure, about 1 μm or less of thephotoresist 118 may remain over the conductive structures 106 andinsulating structures 108, and is subsequently removed. At least onecontact structure may be formed on each of the stairs and coupled, suchas electrically connected through a direct ohmic connection or throughan indirect connection (e.g., via another structure electricallyconnected), to the conductive structures 106 of the tiers 110. Thecontact structures may be formed and coupled to the conductivestructures 106 by conventional techniques, which are not described indetail herein. The contact structures may be coupled (e.g., attached,connected) to routing structures and at least one string driver deviceas known in the art.

The adhesion of the photoresist 118 to the conductive structures 106 andthe insulating structures 108 of the tiers 110 may be further improvedby treating the surfaces of the conductive structures 106 or of theinsulating structures 108 before forming the photoresist 118 thereover.The surface treatment may include, but is not limited to, cleaning thesurfaces of the conductive structures 106 and/or the insulatingstructures 108, forming inorganic spacers on the surfaces of theconductive structures 106 and/or the insulating structures 108,chemically modifying the surfaces of the conductive structures 106and/or the insulating structures 108, nitridating the surfaces of theconductive structures 106 and/or the insulating structures 108, applyingadhesion promoters to the surfaces of the conductive structures 106and/or the insulating structures 108, or applying organic coatingmaterials, such as bottom antireflective coating (BARC), to the surfacesof the conductive structures 106 and/or the insulating structures 108.However, the surface treatment alone (e.g., without also forming therecesses 116) may not be sufficient to adhere the photoresist 118 to theconductive structures 106 or of the insulating structures 108.

As shown in FIG. 10A, which is a SEM of a semiconductor structure formedaccording to embodiments of the disclosure, the photoresist 118 isformed in the recesses 116 of the conductive structures 106. There isgood adhesion (e.g., no delamination) between the photoresist 118 andthe conductive structures 106 and the insulating structures 108.Comparing FIG. 10A to FIG. 10B, which is an enlarged view of FIG. 10A,the recesses 116 formed according to embodiments of the disclosureenable improved adhesion of the photoresist 118 to the tiers 110 and,therefore, the photoresist 118 does not delaminate. A SEM of thestaircase structure at a later stage in the fabrication process is shownin FIG. 11 . No defects in the stairs of the staircase structure areobserved in the circled region. Comparing FIG. 11 to FIG. 5 , thestaircase structure formed according to embodiments of the disclosurehad no deformations in the stairs. Without being bound by any theory, itis believed that the increased surface area provided by the recesses 116within the tiers 110 improves the adhesion of the photoresist 118 to theconductive structures 106 and the insulating structures 108. Theimproved adhesion reduces or eliminates the deformation in the stairs ofthe staircase structure.

The method of improving photoresist adhesion may be used in 3D NANDstructures having staircase structures, such as 3D NAND structureshaving dual decks of staircase structures. While embodiments of thedisclosure describe improving adhesion between a large volume ofphotoresist 118 and materials of alternating conductive structures 106and insulating structures 108 during the fabrication of the staircasestructures, embodiments of the disclosure may be applicable to othersituations in which a large volume of photoresist 118 is to be formed ina slot having relatively large dimensions. By way of example only, theposition of the slot 114 may differ from that shown in FIG. 7 ,depending on the desired position of the staircase(s) ultimately to beformed. As shown in FIG. 12 , a slot 114′ may be formed in a peripheralregion of the alternating conductive structures 106 and insulatingstructures 108 of the staircase structure ultimately to be formed,rather than in an array region as described above. As shown by dashedlines in FIG. 12 , recesses 116 may be formed in the conductivestructures 106 before applying the photoresist 118, as described above,to improve adhesion of the photoresist 118 to the insulating structures108. Alternatively, recesses 116 may be formed in the insulatingstructures 108 before applying the photoresist 118, as described above,to improve adhesion of the photoresist 118 to the conductive structures106.

Embodiments of the disclosure may also be used when a large volume of aspin-on dielectric (SOD) material is to be formed in the slot 114, 114′.Recesses 116 may be formed in the conductive structures 106 or in theinsulating structures 108 before applying the SOD material, as describedabove, to improve adhesion of the SOD material to the conductivestructures 106 or the insulating structures 108.

Additional process acts may be conducted to form the 3D NAND Flashmemory device. For example, a channel material may be formed and extendthrough the alternating conductive structures 106 and the insulatingstructures 108, and memory cells may be formed along the channelmaterial. Such process acts to form the 3D NAND Flash memory device areknown in the art and are not described in detail herein.

The method of improving photoresist adhesion may also be used in theformation of other 3D semiconductor devices, such as in a 3D crosspointmemory device, in which improved photoresist adhesion to conductivematerials and insulating materials is desired.

Accordingly, a method of improving adhesion between a photoresist andconductive or insulating structures is disclosed. The method comprisesforming a slot through at least a portion of alternating conductivestructures and insulating structures on a substrate. Portions of theconductive structures or of the insulating structures are removed toform recesses in the conductive structures or in the insulatingstructures. A photoresist is formed over the alternating conductivestructures and insulating structures and within the slot.

Accordingly, a method of improving adhesion between a spin-on dielectricmaterial and conductive or insulating structures is disclosed. Themethod comprises forming a slot through tiers of conductive structuresand insulating structures on a substrate. Recesses in the conductivestructures or in the insulating structures are selectively formed. Aspin-on dielectric material is formed over the tiers and within theslot.

Accordingly, a method of forming a staircase structure is disclosed. Themethod comprises forming a slot through tiers of conductive structuresand insulating structures on a substrate. Recesses are selectivelyformed in the conductive structures or in the insulating structures. Aphotoresist is formed over the tiers and within the slot and recesses.Repeated trim acts of the photoresist are conducted to form stairs ofthe staircase structure.

While certain illustrative embodiments have been described in connectionwith the figures, those of ordinary skill in the art will recognize andappreciate that embodiments encompassed by the disclosure are notlimited to those embodiments explicitly shown and described herein.Rather, many additions, deletions, and modifications to the embodimentsdescribed herein may be made without departing from the scope ofembodiments encompassed by the disclosure, such as those hereinafterclaimed, including legal equivalents. In addition, features from onedisclosed embodiment may be combined with features of another disclosedembodiment while still being encompassed within the scope of thedisclosure.

What is claimed is:
 1. A method of forming a staircase structure,comprising: forming a slot through tiers of conductive structures andinsulating structures; selectively forming recesses in the conductivestructures or in the insulating structures of the tiers; forming a fillmaterial adjacent to the tiers and within the slot and within therecesses; and conducting repeated trim acts of the fill material to formstairs of the staircase structure.
 2. The method of claim 1, furthercomprising forming a contact structure on each of the stairs of thestaircase structure.
 3. The method of claim 1, wherein selectivelyforming recesses in the conductive structures or in the insulatingstructures comprises conducting a wet etch process or an isotropic,selective dry etch process to selectively etch the conductive structuresor the insulating structures.
 4. The method of claim 1, whereinselectively forming recesses in the conductive structures or in theinsulating structures comprises forming the recesses comprising a widthof from about 1 nm to about 100 nm in the conductive structures or inthe insulating structures.
 5. The method of claim 1, wherein forming afill material adjacent to the tiers and within the slot and within therecesses comprises forming the fill material at a thickness of fromabout 1 μm to about 10 μm.
 6. The method of claim 1, wherein forming aslot through tiers of conductive structures and insulating structurescomprises forming the slot through tiers of polysilicon structures andsilicon dioxide structures.
 7. The method of claim 1, wherein forming aslot through tiers of conductive structures and insulating structurescomprises forming the slot through tiers of tungsten structures andsilicon dioxide structures.
 8. The method of claim 1, wherein forming aslot through tiers of conductive structures and insulating structurescomprises forming the slot through tiers of polysilicon structures andsilicon nitride structures.
 9. The method of claim 1, wherein forming afill material adjacent to the tiers and within the slot and within therecesses comprises forming a spin-on dielectric material over the tiersand within the slot and within the recesses.
 10. A method of forming astaircase structure, comprising: forming a slot through tiers ofconductive structures and insulating structures; selectively formingrecesses in the conductive structures or in the insulating structures;forming a spin-on material over the tiers and within the slot andrecesses, the spin-on material filling the recesses in the conductivestructures or in the insulating structures; and sequentially removingportions of the spin-on material and using the trimmed spin-on materialas a mask to form stairs defined by the underlying conductive structuresand insulating structures.
 11. The method of claim 10, whereinselectively forming recesses in the conductive structures or in theinsulating structures comprises forming the recesses defined bysubstantially vertical sidewalls of the conductive structures or theinsulating structures.
 12. The method of claim 10, wherein selectivelyforming recesses in the conductive structures or in the insulatingstructures comprises forming the recesses defined by non-verticalsurfaces of the conductive structures or of the insulating structures.13. The method of claim 10, wherein selectively forming recesses in theconductive structures or in the insulating structures comprises etchingportions of the conductive structures.
 14. The method of claim 10,wherein selectively forming recesses in the conductive structures or inthe insulating structures comprises etching portions of the insulatingstructures.
 15. A method of forming a staircase structure, comprising:forming a slot through at least a portion of alternating conductivestructures and insulating structures on a material; removing portions ofthe conductive structures or of the insulating structures adjacent tothe slot to form recesses in the conductive structures or in theinsulating structures; forming a fill material laterally adjacent to thealternating conductive structures and insulating structures, the fillmaterial filling the slot and the recesses in the conductive structuresor in the insulating structures; and utilizing repeated fill materialtrim acts to form stairs of the staircase structure.
 16. The method ofclaim 15, further comprising treating the conductive structures or theinsulating structures before forming the fill material laterallyadjacent to the alternating conductive structures and insulatingstructures.
 17. The method of claim 16, wherein treating the conductivestructures or the insulating structures before forming the fill materialcomprises nitridating surfaces of the conductive structures or of theinsulating structures.
 18. The method of claim 16, wherein treating theconductive structures or the insulating structures before forming thefill material comprises applying adhesion promoters to surfaces of theconductive structures or of the insulating structures.
 19. The method ofclaim 16, wherein treating the conductive structures or the insulatingstructures before forming the fill material comprises chemicallymodifying surfaces of the conductive structures or of the insulatingstructures.
 20. The method of claim 15, wherein utilizing repeated fillmaterial trim acts to form stairs of the staircase structure comprisesconducting multiple fill material trim acts to form greater than orequal to one hundred stairs defined by the alternating conductivestructures and insulating structures.